The present invention relates to optical recording discs and more particularly to a hybrid disc having a read-only area (ROM) in which a depth modulated groove is formed and a write once recordable or rewritable area.
Optical recording discs of the write-once or rewritable type include a substrate having a recording layer. The substrate is formed by injection molding to include a wobbled groove on the surface of the substrate where the recording layer is formed. The groove defines recording channels on the disc for recording data and also provides for tracking of the disc while writing or reading data. The groove, which generates a frequency modulated signal after detection and processing, also contains addressing and other information that are necessary for the write and read processes. The groove is usually in accordance with Orange Book specifications. xe2x80x9cOrange Bookxe2x80x9d is a specification published by Philips Corporation and Sony Corporation which defines key properties of recordable compact disc (CD-R) media and recording procedures.
The recording layer, which can include an organic dye, is deposited on the substrate so as to completely cover the groove. The recording layer can be deposited by various techniques, including spin-coating, gravure, roller, flexographic, and vapor phase deposition. A reflective layer is then formed over the entire recording layer using similar techniques. The reflective layer can be, for example, gold, silver, or copper.
Hybrid optical discs are those discs which have a read-only area in which a depth modulated groove is formed and a recordable area. Typically a wobble groove is provided in both areas. As set forth in U.S. Pat. No. 5,696,758 specifies geometry of the wobbled depth modulated groove. The reason for this is that hybrid discs typically have to meet the Orange Book specifications, and it is difficult to achieve these standards with a wobbled depth modulated groove. Particular depths are specified to be in accordance with the Orange Book specifications.
It is an object of this invention to provide a hybrid optical disc which provides improved readability by increasing the tracking signal produced from the wobble groove.
This object is achieved in a hybrid optical recording disc having a substrate and a recording layer disposed over the substrate, the substrate having a read-only (ROM) area in which a groove is modulated by depressions in the substrate and a recordable area in which the groove from the read-only area extends into the substrate in the recordable area, the improvement comprising:
the groove in the read-only area forming wobbling tracks having a depth greater than 170 nm and wherein the depth d2 of the depression in the groove in the read-only area is in a range greater than 170 nm and less than 350 nm.
Another advantage of the present invention is that the conformality of the recording layer on the substrate permits a greater depth of the depressions in the groove than has heretofore been possible while still meeting Orange Book specifications.
In accordance with the present invention the groove in the read-only area forming wobbling tracks is selected to have a depth greater than 170 nm and wherein the depth d2 of the depression in the groove in the read-only area is in a range greater than 170 nm and less than 350 nm. This arrangement provides for improved performance which is within the tolerances of commercial specifications (Orange Book). Moreover, the present invention facilitates the compatibility of both the reading and writing on the hybrid disc.